link reaction and the krebs cycle

• true or false? non-oxygen requiring stages of respiration take place in the cytoplasm and oxygen requiring reactions take place in the mitochondria

  TRUE- glycolysis takes place in the cytoplasm and other stages like the krebs cycle and oxidative phosphorylation take place in the mitochondria
• what is the link reaction also referred to as?

  oxidative decarboxylation
• describe what happens to pyruvate molecules after glycolysis

  • enter mt matrix by active transport using carrier proteins
  • pyruvate undergoes oxidative decarboxylation- carbon dioxide is removed (decarboxylation) along with hydrogen (oxidation). The hydrogen atoms removed are used to reduce NAD
  • once carbon dioxide is removed, this forms a 2C molecule called an acetyl group
  • this acetyl is bound by coenzyme A to produce acetyl CoA (acetyl coenzyme A)
  • acetyl CoA delivers the acetyl group to the next stage of aerobic respiration, called the krebs cycle
  • the reduced NAD formed from the link reaction is used to synthesise ATP in oxidative phosphorylation stage
  • the carbon dioxide produced is removed from the organism as a metabolic waste

  
• true or false. Carbon dioxide is a by-product of the krebs cycle

  TRUE
• describe the process of the krebs cycle

  1. acetyl CoA delivers acetyl group to the krebs cycle
  2. 2C acetyl group combines with 4C oxaloacetate to form a 6C compound
  3. this 6C intermediate undergoes decarboxylation and dehydrogenation twice, producing two $CO_2$ molecules and 2 hydrogens
  4. these hydrogens are used to reduce 2 molecules of NAD forming 2 reduced NAD molecules
  5. this in turn forms a 5C, and then a 4C intermediate
  6. After this, ATP is produced by substrate level phosphorylation a molecule of reduced FAD is produced, and a final molecule of reduced NAD is produced
  7. the cycle begins again as the 4C oxaloacetate is regenerated

  
• why are coenzymes like NAD and FAD important in respiration?

  • transfer electrons and protons between reactions
  • to other enzymes in later stages of respiration
  • needed because otherwise respiratory enzymes wouldn't be able to function
• what are the differences between NAD and FAD

  • NAD takes part in all stages of respiration whereas FAD takes part in only the krebs cycle
  • reduced NAD is oxidised at the start of the ETC releasing protons and electrons whereas FAD is oxidised further along the chain
  • reduced NAD results in the synthesis of three ATP molecules, but reduced FAD results in the synthesis of two ATP molecules
• state the products of the krebs cycle

  • 1 ATP molecule
  • 3 molecules of reduced NAD
  • 1 molecule of reduced FAD
  • 2 carbon dioxide molecules
• true or false? coenzymes aren't derived from vitamins

  FALSE- they are